What is Non-linear Static Push-over Analysis?
The pushover analysis of a
structure is a static non-linear analysis under permanent vertical loads and
gradually increasing lateral loads. The equivalent static lateral loads
approximately represent earthquake induced forces. A plot of the total base
shear versus top displacement in a structure is obtained by this analysis that
would indicate any premature failure or weakness. The analysis is carried out
upto failure, thus it enables determination of collapse load and ductility
capacity. On a building frame, and plastic rotation is monitored, and lateral
inelastic forces versus displacement response for the complete structure is
analytically computed. This type of analysis enables weakness in the structure
to be identified. The decision to retrofit can be taken in such studies.
The seismic design can be viewed as a two step process. The first, and usually
most important one, is the conception of an effective structural system that
needs to be configured with due regard to all important seismic performance
objectives, ranging from serviceability considerations. This step comprises
the art of seismic engineering. The rules of thumb for the strength and
stiffness targets, based on fundamental knowledge of ground motion and elastic
and inelastic dynamic response characteristics, should suffice to configure
and rough-size an effective structural system.
Elaborate mathematical/physical models can only be built once a structural
system has been created. Such models are needed to evaluate seismic
performance of an existing system and to modify component behavior
characteristics (strength, stiffness, deformation capacity) to better suit the
specified performance criteria.
The second step consists of the design process that involves demand/capacity
evaluation at all important capacity parameters, as well as the prediction of
demands imposed by ground motions. Suitable capacity parameters and their
acceptable values, as well as suitable methods for demand prediction will
depend on the performance level to be evaluated.
The implementation of this solution requires the availability of as set of
ground motion records (each with three components) that account for the
uncertainties and differences in severity, frequency characteristics, and
duration due rapture characteristics distances of the various faults that may
cause motions at the site. It requires further the capability to model
adequately the cyclic load-deformation characteristics of all important
elements of the three dimensional soil foundation structure system, and the
availability of efficient tools to implement the solution process within the
time and financial constraints on an engineering problem.
Purpose of Push-over Analysis